To remove debris from a surface such as a parking lot, city street, and the like, mobile, truck or trailer mounted sweepers may be used. Such sweepers typically use forced air currents, rotating brushes or a combination of air currents and brushes to sweep the debris from the surface and into a hopper for collection. Known prior art sweepers generally do a satsifactory job of removing most, if not all, of the debris. However, certain problems remain due to the varying nature of the debris found in parking lots, city streets, and the like. While one type of sweeper may be excellent for removing relatively light, low density debris, e.g., paper and dust, it may be incapable of picking up heavier debris, e.g., broken glass, sand and gravel. Oftentimes the design of certain prior art sweepers allows the forced air currents to concentrate above the ground surface, thereby leaving the heavier debris on the ground undisturbed. This shortcoming has been overcome in many prior art sweepers by increasing the system's airflow and adding dust control skirting. The increased airflow consumes excess power and accelerates the wear of the airflow systems components.
The present invention is believed to overcome the shortcomings of the known prior art in that it allows a single pick-up head in a single pass over a surface to simultaneously pick up debris of varying sizes and densities by controlling air velocity without increasing the total system cubic feet per minute air flow and power consumption. An air velocity control mechanism is provided in the pick-up head which allows selective removal of a wide range of debris sizes and densities. Further, the invention provides an increase in breadth of the sweeping path, in that the construction and arrangement of the pick-up head allows the forced air flow to sweep the full width of the pick-up head.